Is It Okay to Cook Veggies?

The New York Times is looking for the best way to cook vegetables. More from Tara Parker-Pope:

Surprisingly, raw and plain vegetables are not always best. In The British Journal of Nutrition next month, researchers will report a study involving 198 Germans who strictly adhered to a raw food diet, meaning that 95 percent of their total food intake came from raw food. They had normal levels of vitamin A and relatively high levels of beta carotene.

But they fell short when it came to lycopene, a carotenoid found in tomatoes and other red-pigmented vegetables that is one of the most potent antioxidants. Nearly 80 percent of them had plasma lycopene levels below average.

“There is a misperception that raw foods are always going to be better,” says Steven K. Clinton, a nutrition researcher and professor of internal medicine in the medical oncology division at Ohio State University. “For fruits and vegetables, a lot of times a little bit of cooking and a little bit of processing actually can be helpful.”

The amount and type of nutrients that eventually end up in the vegetables are affected by a number of factors before they reach the plate, including where and how they were grown, processed and stored before being bought. Then, it’s up to you. No single cooking or preparation method is best. Water-soluble nutrients like vitamins C and B and a group of nutrients called polyphenolics are often lost in processing. For instance, studies show that after six months, frozen cherries have lost as much as 50 percent of anthocyanins, the healthful compounds found in the pigment of red and blue fruits and vegetables. Fresh spinach loses 64 percent of its vitamin C after cooking. Canned peas and carrots lose 85 percent to 95 percent of their vitamin C, according to data compiled by the University of California, Davis.

Fat-soluble compounds like vitamins A, D, E and K and the antioxidant compounds called carotenoids are less likely to leach out in water. Cooking also breaks down the thick cell walls of plants, releasing the contents for the body to use. That is why processed tomato products have higher lycopene content than fresh tomatoes.

Now, Dr. Fuhrman is sensitive about this subject. We’ve got a whole post on it. Here’s a bit from The Cold Truth About Raw Food Diets:

Cooking can be beneficial.
In many cases, cooking destroys some of the harmful anti-nutrients that bind minerals in the gut and interfere with the utilization of nutrients. Destruction of these anti-nutrients increases absorption. Steaming vegetables and making vegetable soups breaks down cellulose and alters the plants’ cell structures so that fewer of your own enzymes are needed to digest the food, not more. The point is that this “cooked food is dead food” enzyme argument does not hold water. On the other hand, the roasting of nuts and the baking of cereals does reduce availability and absorbability of protein.

Low-temperature cooking.
When food is steamed or made into a soup, the temperature is fixed at 100 degrees Celsius or 212 Fahrenheit—the temperature of boiling water. This moisture-based cooking prevents food from browning and forming toxic compounds. Acrylamides, the most generally recognized of the heat-created toxins, are not formed with boiling or steaming. They are formed only with dry cooking. Most essential nutrients in vegetables are more absorbable after being cooked in a soup, not less absorbable. Recent studies confirm that the body absorbs much more of the beneficial anti-cancer compounds (carotenoids and phytochemicals—especially lutein and lycopene) from cooked vegetables compared with raw. The Institute of Food Research in Norwich reported their recent findings in New Scientist magazine: about 3 to 4 percent of the carotenoids were absorbed from raw carrots compared with about 15 to 20 percent from cooked and mashed carrots. The team also found that we absorb these critical anti-cancer nutrients more effectively from vegetables than we do from supplements.

Multiple studies have demonstrated that the beneficial antioxidant activity of cooked tomatoes is significantly higher than from uncooked tomatoes. Scientists speculate that the increase in absorption of antioxidants after cooking may be attributed to the destruction of the cell matrix (connective bands) to which the valuable compounds are bound.

Good, because if I go a few days without steamed broccoli, I get the shakes—GIVE ME MY BROCCOLI!

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Comments (6) Read through and enter the discussion with the form at the end
Michael - May 21, 2008 11:16 AM

Here's a question: is it better to cook vegetables long and slow at a low heat (like a crock-pot) or the more rapid water-based method of pressure-cooking that would elevate temperatures above 212 degrees F but for a much shorter time?

Gerry Pugliese - May 21, 2008 12:25 PM

Hey Michael-

Good question. Personally, I water sautee and steam most of my food, but, in the office team Fuhrman pressure cooks a lot.

I'll forward your comment to the big dog. I'll keep you posted.


LolaBloom - May 21, 2008 6:09 PM

I'm pretty new to raw foods but most everything I've read states it is considered raw as long as it's not heated to over 118 degrees (I might be off on that number a teeny bit)...

So what are we categorizing as raw vs cooked in this article? I think blanketly stating any heat = cooked isn't 100% accurate and is it possible for the same benefits to be acheived when the food is exposed to low temps (under 118 or whatever the magic # is) and therefore it's still considered raw? And is it to say that even at high temps that the benefits remain and don't eventually get exposed to too much heat?

That's the part I'm researching more myself and not getting lots of info on....I like warmed up foods just as the next guy and would like to incorporate more "raw" but trying to get the facts because ultimately, I'm trying to eat for HEALTH and if heating to a certain temp retains that and over a certain temp removes the nutrients, I'd surely like to know!

Sara - May 22, 2008 8:56 AM

Lola- steaming or making soup isNOT heating at below 118 degrees. Some nutrients are better absorbed when food is cooked. That 118 thing is a raw foodist idea not a scientific fact. We eat both raw and cooked vegetables. Refer to Dr. Fuhrman's previous post on subject.

Joel Fuhrman, MD - May 25, 2008 1:24 PM


It is better to eat lots of foods raw and some foods (soups with greens, tomatoes, beans) water cooked. Slow cooking versus faster cooking is not the issue and will not make much of a difference.

Louise - May 26, 2008 11:16 PM

According to a March 2007 study published the The Journal of Food Science, steaming and boiling caused a 22 to 34% loss of vitamin C; Microwaved and pressure-cooked vegetables retain 90% of their vitamin C. That's in the article.

That's what I already do: microwave and pressure cook - yay!

Interesting side point: "When the salsa or salad was served with fat-rich avocados or full-fat salad dressing, the diners absorbed as much as 4 times more lycopene, 7 times more lutein and 18 times the beta caratene than those who had their vegetables plain or with low-fat dressing."

So I need to improve to add fat instead of just eating a lb of lettuce out of the bag . . .

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